Mg2Si热电材料力学性能的分子动力学模拟研究:纳孔效应

在热电材料里引入纳孔能有效降低材料的热导率从而提高其热电性能,但纳米孔洞的引入也可能影响材料的力学性能。以圆柱孔理想单晶Mg_2Si块体热电材料为研究对象,建立不同孔径、孔隙率以及分布形式的纳孔Mg_2Si材料的原子模型,采用分子动力学模拟方法研究不同模型下材料的拉伸力学性能。结果表明:①纳孔的引入造成Mg_2Si热电材料的极限应力和弹性模量的降低,而纳孔孔隙率、分布形式都会影响到材料的极限应力,而材料的弹性模量主要与孔隙率有关,孔隙率越大,材料的弹性模量越低;②纳孔的引入不仅减小材料的有效荷载面积,更重要的是造成材料内部应力分布不均匀,而材料所能承受的拉伸方向的应力极限是一定的,因而当纳孔Mg_2Si热电材料平均应力远小于完整块体的极限应力时,材料内部最薄弱的地方的应力就已达到其极限应力,造成材料的破坏。

Molecular dynamics simulation study of the effects of nanopores on the mechanical properties of Mg2Si

The introduction of nanopores in thermoelectric materials can effectively reduce the thermal conductivity of materials so as to improve the thermoelectric performance, but also the introduction of the nanopores may affect the mechanical properties of materials. Based on the research object of ideal single crystal Mg2Si thermoelectric materials with cylindrical nanopores , establish Mg2Si material calculation model with different diameter ,porosity and distribution of nanopores, using molecular dynamics simulation method study mechanical properties of different models under uniaxial tensile. The results showed that: 1 introduction of the nanopores in Mg2Si thermoelectric material make ultimate strength and Young"s modulus decreased, the distribution and porosity of nanopores will affect the ultimate strength of material, but Young"s modulus of materials mainly related to the porosity, the greater the porosity, the lower Young"s modulus of the material. 2 the introduction of nanopores not only reduces effective load area of material, what more important , cases uneven distribution of inner stress in the material,but the strength limit the material can withstand in the tensile direction is certain, so when the Mg2Si thermoelectric materials with nanopores mean stress is far less than ultimate stress of a complete block material , the internal stress of the weakest part in it has reached its limit stress, thus causing the destruction of the material.